Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TITLE
POWER SAVER CONTROLLER
TECHNICAL FIELD
This invention relates to the control of the supply of electrical power to
plug-in electrical equipment, in particular to the control of the supply of
electrical power to groups of such electrical equipment where the power
supply requirement of these groups is related to the operational status of a
main piece of electrical equipment. More particularly it relates to the
provision of electrical power to peripheral devices in a personal computer
installation.
BACKGROUND ART
A desktop computer installation typically has associated with it a number of
peripheral devices and other associated electrical devices, each of which is
separately electrically powered. The peripheral devices can include such
things
as printers, scanners and modems or there may be associated devices such as
a desk lamp or a room heater.
These peripheral devices and associated electrical equipment are in general
not
used when the computer is not in use. However, because they are separately
electrically powered the user must, when turning off the computer, also turn
off
each of the peripheral and associated devices. This is a time consuming
process and indeed given.the placement of the power switches on many such
electrical devices, may be extremely inconvenient.
It is also the case that widely used computer operating systems require
significant time to perform certain "housekeeping" tasks in between receiving
command to shut down and actually shutting off the power or being in a
position
to have the power supply to the computer shut off without causing problems for
the computer system. During this time, the computer system also may not
tolerate having power removed from peripheral devices.
Accordingly many users simply leave the additional devices powered on after
the computer has been shut down.
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This is not ideal for a number of reasons. The first of these is that the
devices
continue to consume power which is both costly and a waste of resources. This
is particularly a problem since many modern devices use small plug-in
transformers to provide the lower operating voltages which they require. These
plug-in transformers continue to consume power whilst they are connected to a
mains supply even if the power switch on the device which they are supplying
with power has been switched off.
It is also the case that all electrical devices have a finite life span of
operation and
this life span can be made to extend over a longer period of time if the
device is
switched off when not in use.
It is also advantageous that mains power be removed from devices when not
required in order to reduce the possibility of exposure to damaging surges in
the mains power supply.
Prior art devices hav_e attempted_todeal_.with
this_.problem..by_providing_r_ela.y_s_.__-_____
which cut off power to peripheral devices when no current is flowing to the
main
device, the main device being the desktop computer itself.
However, most modern desktop computers have the ability to control their
power usage to some extent by entering one or more lower power
consumption states, usually referred to as standby states. Users may allow the
device to spend extended periods in such a standby state, negating most of
the advantages of the prior art devices.
DISCLOSURE OF THE INVENTION
Accordingly there is proposed in one form of the invention, a power supply
control device for permitting energisation of a plurality of electrical
devices from a
single mains supply electrical outlet characterized in that there are provided
a
plurality of controlled electrical outlets and a single electrical input
adapted to
connect to a mains supply electrical output; switch means adapted to connect
electrical supply from the supply electrical outlet to each of the controlled
electrical outlets in response to the state of a master electrical device, a
state
sensor adapted to detect a functional state of a master electrical device,
said
sensor being adapted to distinguish at least three functional states of the
master
device.
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In preference the three functional states of the master device are off, a
reduced
power state hereafter called "standby", and a fully on state.
The state sensor may use one or more of a number of possible means to
detect the state of the master device. These may include the direct receipt of
digital information from the master device indicating its actual or intended
functional state.
It may also include connection to any one or more of the output ports of the
master device which may include serial or parallel communication ports, USB
ports, or any other port.
In preference the state sensor is adapted to sense the power consumption of or
current flow to, the master device.
The modern desktop computer generally has a complex and relatively time
consuming "power up sequence" which is the series of activities which the
computer performs immediately upon being first switched on. This sequence
may include activities to discover what peripheral devices are connected to
the
computer and to establish communication with such peripherals. One of the
advantages of the standby mode is that it is not necessary for the computer to
go through this power up sequence when it emerges from standby into fully
powered mode.
However, this has the problem that some types of peripheral device cannot be
switched off while the computer is in standby mode or the computer will lose
the
ability to communicate with such devices until a full power on sequence is
performed.
Accordingly the controlled electrical outlets are controlled such that at
least one
controlled electrical outlet continues to provide an electrical power supply
while
the state sensor indicates that the master electrical device is in a standby
condition.
In preference, at least one controlled electrical outlet is controlled such
that it does
not provide an electrical supply when the state sensor indicates that the
master
electrical device is in a standby state, but only when the state sensor
indicates
that the master electrical device is in a fully on state.
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For example, a modem or an external disk drive would be connected in such a
manner that power was not withdrawn from them when the computer is in a
standby mode but a printer or a desk lamp might be connected such that they
receive power only when the computer is in a fully on mode.
Depending on the individual computer and its particular hardware
configuration,
the current or power drawn by the computer when in its standby mode may
vary.
In preference then, the state sensor is adapted to permit the threshold power
or
current level at which it will indicate that the master electrical device is
in a standby
mode to be field resettable.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described with reference to drawings wherein:
Figure 1 is a pictorial representation of an embodiment of the invention,
Figure 2 is a block diagram showing the main functional blocks of an
embodiment of the invention,
Figure 3 is a circuit diagram of an embodiment of the invention, and
Figure 4 shows a circuit diagram of a further embodiment of the invention.
BEST MODE FOR CARRYING OUT THE INVENTION
Turning now to Figure 1 there is shown a perspective drawing of a power
supply control device according to an embodiment of the invention. There is a
box 100 containing the working circuitry of the device. There is a power cord
101 which is connected to a general-purpose electrical outlet. There is a
power
outlet 102 which is in permanent electrical connection with the mains power
supply to the device. There is a power outlet 104 which is available to have
connected to it such electrical loads as require power only when the main
computer is in a full power mode. A power board or power strip 107 is
connected to this outlet in order to allow multiple devices to be powered in
this
manner. Exemplary devices of this class, being a printer 112 and a desk lamp
113 are shown.
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There is a further electrical outlet 103 which is available for the connection
of
loads which require power when the computer is in a fully on or a standby mode
but which do not require power when the main computer is switched off. A
further power board or power strip 108 is connected to this outlet in order to
5 allow multiple devices to be powered in this manner. An exemplary device of
this type is a modem 109.
Further there is a connection port 105 for the connection of a serial
communications cable to the device. A switch 106, called the "learn" switch,
is
provided for communicating to the device the fact that the standby threshold
should be reset:
Considering Figure 2, the main functional blocks of the device can be seen in
block diagram form. There is a mains power inlet 201 which supplies.power to
a low voltage power supply 202. This supply provides power for the device's
electronic components. Mains power is also supplied to the PC power module
203 which provides a non switched output 204 for powering the main electrical
device which would usually be a desktop computer. A surge suppressor 202
protects the circuitry from mains power surges.
Mains power is also provided to controlled outputs 205 and 206 via switch
means 207 and 208. The power supply to the non switched outlet 204 is
monitored via state sensor 209. The state sensor provides signals proportional
to the current and voltage drawn by the desktop computer to input 210 and 211
of microcontroller 212.
The microcontroller 212 processes the signals and produces output signal 213
to turn on first controlled switch 207 only when the power drawn by the
desktop
computer is such that it exceeds a threshold value set to indicate that the
computer is fully on and not merely in a standby state.
A signal is produced at output 214 to turn on second controlled switch 208
when
the power drawn by the desktop computer is above a threshold indicating that
the desktop computer is on but in a standby mode.
Thus first controlled switch 207 is on only when the computer is fully on,
while
second controlled switch 208 is on when the computer is in either a fully on
state
or a standby state.
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There is also provided a communications module 215 which allows direct data
communication between the desktop computer and the power controller device.
This may be used to update the microcontroller firmware to set or alter any
variables held within the microcontroller, or to allow the computer to
directly take
on the function of the voltage and current detectors 209 and 210 and directly
control switches 207 and 208
Figure 3 shows a circuit diagram of an embodiment of the invention. There is a
mains power supply plug which provides power to the power supply device
and also is the source of the power supply which is switched by the device to
the peripheral and associated devices of the computer installation.
There is a low voltage power supply which is shown as block 7. This is made
up of a fuse 2, a transformer 3 which has a mains voltage primary coil and two
nine-volt secondary coils. DC rectification is provided by a bridge rectifier
4 and
a linear voltage regulator 6. This provides a stable five-volt DC power
supply.
The surge suppression circuitry 30 is connected in parallel with the power
supply. It provides surge suppression using three metal oxide varistors 29
wired in a delta configuration to limit the maximum voltage between any two
wires to the breakdown rating of the varistors.
The supply of power to the desktop computer which is supplied via the device
of the invention, but is not switched by the device, is provided by power
outlet
9. The neutral connection to this plug includes current sensing resistor 8.
There
is a current signal conditioning differential input amplifier 10. This
transfers the
reference for the current signal from neutral to earth. If this is not done
the neutral
connector would need to be connected to the common terminal of the power
supply. Through any serial port cornnection, this would be connected to the
neutral or earth conductor of the computer's internal power supply, which
could
cause unwanted tripping of residual current devices protecting the circuit.
The value of resistor 8 is chosen to be very low in order to reduce the power
dissipated in the resistor. Accordingly there is a requirement for a current
signal
amplifier 11 in order to provide a referenced signal of sufficient magnitude.
The
gain of this amplifier may be varied under the control of microcontroller 24
by
controlling analogue switches 12 in order to place one or more of resistors 13
in
or out of circuit.
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The current signal is further conditioned by the signal conditioning circuitry
31. A
capacitor eliminates any DC offset in the amplifier output while a resistor
and two
diodes provide a current limit and voltage clamping so that the amplified
current
signal is in a fixed range about a reference voltage VAref, being the voltage
at
60. The signal range is -.3V to VAref +0.3V. The current detection signal is
then
applied to analogue to digital converter input 51 of the micro controller 24.
The incoming active and neutral are connected to the resistive divider 14 for
the
purposes of detection of the voltage applied to the desktop computer.
Differential amplifier 15 shifts the reference for the voltage signal from
neutral to
earth in the same manner as is done by differential input amplifier 10 for the
current signal.
The voltage signal is then applied to a conditioning circuit 16 which includes
a
current limiting resistor and clamping diodes which limit the signal to -.3v
to var ref
+0.3v. The signal is applied to input 52 of the micro controller 24 which is
configured to be the second channel of an analogue to digital converter.
A zero crossing detector 17 provides a signal to the micro controller 24 when
the
voltage is at zero. This allows the micro controller to ensure that
measurements
of the voltage and current signals are synchronised. A voltage reference is
provided by an active precision voltage reference 23. This reference voltage
is
applied to the microcontroller to fix the upper limit of the analogue to
digital
converter.
Serial communications circuitry 22 allows for the connection of an RS 232
serial
port. Solid-state relays 27 control the supply of power to switched power
outlets 25, 26. The signals to switch the solid-state relay 27 are provided
from
the micro controller 24 via transistor buffers 28. The switch 33 is provided
to
connect the interrupt input 53 of the micro controller 24 to ground when the
switch
is activated. Software in the micro controller monitors the current/power
consumed by the desktop computer and it controls the power outlets 25 and
26.
The microcontroller attempts to automatically detect and establish power
levels
which correspond to the standby mode and fully off mode of the desktop
computer.
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Based on historical performance the software within the microprocessor
determines which power levels correspond to the standby mode and the shut
down model of the desktop computer and stores these values into e-prom.
When the threshold value for standby is exceeded output 26 is energised,
when the power threshold for the on mode is exceeded then both outputs 25
and 26 are energised.
These automatically determined values can be overwritten. This is achieved by
pressing the "learn" switch 106 to place the device into a learning mode, and
then placing the desktop computer into a standby state. The switch 106 is then
pressed again. The value of the power being consumed by the desktop
computer at this time is measured and this value is stored as the standby
threshold. The PC is then switched off and the switch 106 pressed again. The
micro controller stores this new level of current/power as the threshold
indicating
that the main computer is off.
The desktop computer power consumption is calculated by taking the voltage
signal and the current signal which are applied to input 51 and 52 of the
micro
controller and multiplying the corresponding samples and applying the relevant
calculation to calculate power. This power measurement gives a much more
accurate indication of the power consumption of the desktop computer than a
simple current measurement as it also takes into account any phase shift
between the current and the voltage as well as waveshape.
Figure 4 shows a further embodiment of the invention. This circuit operates in
the same manner as that of Figure 3, with the variations described below.
In some circumstances a user may require that power be withdrawn from the
computer as well as the peripheral devices when the computer is turned off.
This may be because, with modern computer power supplies which are
software switched, the computer will continue to draw a small amount of power
even when it has been instructed to switch off. Alternatively, some users are
simply more comfortable with the knowledge that the computer is isolated from
the mains power supply.
In this embodiment, the unswitched power outlet 9 is replaced by a power
outlet 511 where the power supply to this outlet is controlled by the
microprocessor 24 via solid state relay 512. This operates to remove power
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from outlet 511 as well as from outlets 25 and 26 when the microprocessor
detects that the computer has shutdown.
When this occurs, the computer ON/OFF switch is ineffective, since there is no
power to the outlet 511 to which the computer is connected. In order to turn
on
the PC, the interrupt switch 33 is pressed which causes power to be supplied
to power outlet 511 for a brief period (ten seconds in this case). If the PC
is
switched on during this time, current begins to be drawn through outlet 511
and
the power control device is able to operate, supplying power to outlets 511,
25
and 26 as appropriate.
A user may not wish this total shut down of power to occur. Accordingly, there
is
firmware provided to allow for two modes of operation. In one mode the switch
512 operates as described above. In the second mode, switch 512 is always
on an the device behaves in the same manner as the circuit of figure 3. The
firmware for the microprocessor 24 allows the interrupt switch 33 to be used
to
.15 communicate.which mode is to be employed. An interrupt extension socket
517 is provided to allow the interrupt switch to be placed remotely from the
main power control device.
As illustrated in the circuit of Figure 4, the current sensing resistor 8 may
be
replaced by a current transformer 510This has the advantage that the current
sense signal is electrically isolated from the mains voltage. This eliminates
the
need for the current signal conditioning amplifier.
Differential amplifier 15 is also eliminated by providing a mains voltage
sensor
516 which is connected to the power supply transformer 3. This mains voltage
sensor provides a mains voltage signal to the conditioning circuit 16 which is
as
described for the embodiment of figure 3.
An output of the microprocessor 24 is used to drive Light emitting diode 502
to
indicate the operational status of the device. A buzzer 504 is also provided
under the control of the microprocessor 24 to allow status messages to be
communicated to an operator.
A switch 503 is provided to signal to the microprocessor that it should enter
a
programming mode to allow reception of firmware upgrades.
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The signal from the current transformer 510 is applied to current signal
amplifier
513. The gain of this amplifier is controlled by the microprocessor 24 by
using
control lines 514 to connect selected resistors 515 into the earth path of the
amplifier.
5 Although the invention has been herein shown and described in what is
conceived to be the most practical and preferred embodiment, it is recognised
that departures can be made within the scope of the invention, which is not to
be
limited to the details described herein but is to be accorded the full scope
of the
appended claims so as to embrace any and all equivalent devices and
10 apparatus.
,
